This invention relates generally to low temperature or cryogenic refrigeration and, more particularly, to pulse tube refrigeration.
The cooling, liquefaction and/or subcooling or densification of certain gases such as neon, hydrogen or helium requires the generation of very low temperature refrigeration. For example, at atmospheric pressure neon liquefies at 27.1 K, hydrogen liquefies at 20.39 K, and helium liquefies at 4.21 K. The generation of such very low temperature refrigeration is very expensive. Inasmuch as the use of fluids such as neon, hydrogen and helium are becoming increasingly important in such fields as energy generation, energy transmission, and electronics, any improvement in systems for the liquefaction of such fluids would be very desirable.
A recent significant advancement in the field of generating low temperature refrigeration is the pulse tube system wherein pulse energy is converted to refrigeration using an oscillating gas. Such systems can generate refrigeration to very low levels sufficient, for example, to liquefy helium. However, such refrigeration generated by pulse tube systems is very costly if the starting point is a relatively high temperature such as ambient temperature.
Accordingly, it is an object of this invention to provide a system for providing cryogenic refrigeration using a pulse tube system which can more efficiently provide such refrigeration than can heretofore available systems using pulse tube technology.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for providing refrigeration to a heat load comprising:
(A) compressing pulse tube gas to produce hot compressed pulse tube gas, cooling the compressed pulse tube gas, and expanding the cooled pulse tube gas to produce cold pulse tube gas;
(B) warming the cold pulse tube gas by indirect heat exchange with heat transfer medium to produce cooled heat transfer medium, and warming the cooled heat transfer medium by indirect heat exchange with refrigeration fluid to produce cooled refrigeration fluid at a first temperature within the range of from 10 to 280 K;
(C) providing refrigeration into the cooled refrigeration fluid to produce cold refrigeration fluid at a second temperature lower than said first temperature and within the range of from 3 to 150 K; and
(D) warming the cold refrigeration fluid by passing refrigeration from the cold refrigeration fluid into a heat load.
Another aspect of the invention is:
Apparatus for providing refrigeration to a heat load comprising:
(A) a pulse tube refrigerator comprising a regenerator body, a pulse tube body having a pulse tube heat exchanger, means for generating pressurized gas for oscillating flow within the regenerator body, and means for expanding gas within the pulse tube body through the pulse tube heat exchanger;
(B) a forecooling circuit comprising a forecooling heat exchanger, means for passing heat transfer medium from the pulse tube heat exchanger to the forecooling heat exchanger, and means for passing heat transfer medium from the forecooling heat exchanger to the pulse tube heat exchanger;
(C) means for passing refrigeration fluid to the forecooling heat exchanger, and means for providing refrigeration into the refrigeration fluid downstream of the forecooling heat exchanger; and
(D) a heat load and means for passing refrigeration from the refrigeration fluid into the heat load.
As used herein the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the term xe2x80x9cdirect heat exchangexe2x80x9d means the transfer of refrigeration through contact of cooling and heating entities.
As used herein the term xe2x80x9cmagnetizexe2x80x9d means to induce magnetic properties to a substance by use of an externally applied electrical field.
As used herein the term xe2x80x9cheat loadxe2x80x9d means an entity at a higher temperature capable of receiving refrigeration and thus being cooled to a lower temperature.